Uber, the smartphone app that hails taxis, is lowering some prices temporarily to get more customers riding during the slower winter months.

The company lowered prices for its UberX service by 2% to 30% in some areas for a trial period, Chief Executive Travis Kalanick said. The traditional Uber service involves a black car and a professional driver, while UberX uses amateur drivers in regular cars.

Both kinds of drivers work for themselves or independent limo services, normally paying Uber a 20% cut of the fares generated by the app. Like taxis, Uber’s fares include a base fee as well as rates based on time and mileage, which vary from city to city. In its largest cities, fares for Uber rides totaled more than $100 million in 2013 before the company took its cut, Kalanick has previously said.

In separate emails Thursday explaining the price changes, Uber told drivers in San Francisco that it expected to “raise the rates back after the promotion,” while it told customers in the city that the change would be in effect until further notice. In an interview, Kalanick said the lower fares could become permanent in some areas. The company told San Francisco drivers it would pay for the reduced prices by taking a lower commission of 5%.

The lower rates will have little bearing on “surge” pricing, where passengers sometimes pay double or more over the cost of a usual ride. Despite customer protests, that’s not going away – as Kalanick has made clear. He said surge pricing motivates drivers to get on the road during times of peak demand.

Cutting the prices of Uber’s cheapest service may help it stave off competition from rivals Lyft and Sidecar, which have managed to grab some of the market for low-cost rides by deploying armies of regular car owners who want to make a few bucks sharing a ride.

An average trip from San Francisco’s Marina district to the Financial District is now about $10.35 using UberX – down from about $12 before, according to Kalanick. That compares with a fare of about $14.70 in a yellow taxi, the CEO says.

“We are creating everyone’s private mass transit option,” Kalanick says. “We are creating an option that is so inexpensive that it can often replace mass transit.”

In a few cities, the lower prices are coming out of Uber’s pocket, he said. Elsewhere, it will mean lower pay for Uber’s drivers, which Kalanick expects will be offset by increased demand. “We get more trips per hour in all the cases we have [lowered fares] so far, and the increase in more trips per hour has turned into more income for the driver,” he said.

Lyft, for its part, has offered a slew of discounts to get new riders using its app. In 13 cities where it operates, Lyft gives new customers unlimited free rides for two weeks if they agree to give drivers feedback after each trip. And for special occasions, like Halloween, the company has armed its drivers with baskets of Lyft discounts to give to riders.

Kalanick said UberX now has the lowest prices of all ride-sharing apps. But John Zimmer, co-founder of Lyft, said the higher rates Uber charges in times of great demand make it the more expensive service. Lyft also began using surge pricing recently in some cities, but caps the amount it charges at three times the normal fare.

Sidecar CEO Sunil Paul said Uber is more expensive on average, and that his company gives riders the exact cost before booking. “We believe consumers deserve this kind of price transparency,” he said.

To see which car-sharing app is cheaper in your city, you can compare Uber’s rates here and Lyft’s rates here. Sidecar doesn’t share information about its rates.